Optical signals transmitted in a fiber optic communication system typically constitute a series of pulses of digital information. Although the pulses are usually at a single nominal wavelength, each pulse is composed of different spectral components, which propagate through the transmission fiber at different speeds. This effect, known as “chromatic dispersion”, can result in spectral components of one pulse arriving at a receiver at substantially the same time as a succeeding pulse, thereby causing degraded receiver sensitivity and higher bit error rates. Chromatic dispersion becomes increasingly pronounced at higher bit rates, e.g. 10 Gigabits/second and higher.
Many transmission optical fibers are non-dispersion shifted and have a “positive” chromatic dispersion, whereby higher frequency components travel slower than lower frequency components. Accordingly, dispersion compensated fiber (DCF) having a negative dispersion can be coupled to the transmission optical fiber in order to offset the chromatic dispersion thereof. The amount of dispersion experienced by an optical signal depends on the distance traveled through the transmission optical fiber. For longer transmission fiber lengths, more compensation, and, thus, longer lengths of DCF are required. Shorter lengths of DCF, however, are provided when less compensation is needed.
In a fiber optic network, different lengths or spans of transmission optical fiber are used to connect various points within the network. In addition, various components inserted into the optical transmission path, such as optical add-drop multiplexers (OADMs) can contribute to the chromatic dispersion associated with a particular span. If the network contains many spans, the dispersion associated with each span must be measured, which can be time consuming.